Color signal converter, display unit, color signal conversion program, computer-readable storage medium storing color signal conversion program, and color signal conversion method

ABSTRACT

A color conversion circuit converts a three-primary-color signal PS 0  to a 5-color signal PS 5,  and includes (i) a color component extraction module that generates, by performing isochromatic conversion, a 7-color signal PS 2  made up of 7 color components equivalent in terms of color to color components d 1  through d 5  of the 5-color signal PS 5,  and (ii) a matrix operation module that generates color components of the 5-color signal by performing linear combination of the color components of the 7-color signal. With this, it is possible to realize a color conversion circuit by which colors represented by a signal after conversion can be adjusted using intuitively-understandable parameters.

This Nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application No. 2004-79258 filed in Japan on Mar. 18, 2004 andPatent Application No. 2005-44669 filed in Japan on Feb. 21, 2005, theentire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to signal processing for processing acolor video signal and the like, and particularly relates to colorsignal conversion by which a trichromatic (three-primary-color) signalis converted to a color signal corresponding to not less than fourcolors. The present invention also relates to a color display apparatusand color display method for displaying color images.

BACKGROUND OF THE INVENTION

Color display apparatuses (display apparatuses) such as color TV setsand color monitors typically reproduce colors by subjecting RGB primarycolors to additive color mixing. A typical example of a video signalsupplied to such display apparatuses is a three-dimensional (e.g. RGBand YCrCb) color video signal (video signal).

In the meanwhile, a display apparatus that subjects not less than fourprimary colors to the additive color mixing has also been proposed. Avideo signal supplied to such a display apparatus is typically requiredto be made up of primary-color signals corresponding to the respectiveprimary colors reproduced by the display apparatus. This type of videosignal, however, is not in widespread use, and hence it is necessary tospecially generate such a video signal.

For this reason, there are needs for a technology to convert awidely-used video signal made up of three primary-color signals to avideo signal made up of multi-primary-color signals corresponding to notless than four primary colors.

According to Japanese Laid-Open Patent Application No. 6-261332/1994(published on Sep. 16, 1994; Patent Document 1), for instance, amulti-primary-color video signal is obtained in such a manner that, (i)it is identified where an RGB three-primary-color video signal havingbeen supplied locates on a chromaticity diagram, (ii) in accordance withthe result of the identification, three primary colors are suitablyselected from more than three primary colors, and (iii) a linearcombination of the selected primary colors is obtained.

The technology taught by Patent Document 1 can realize relativelyprecise color reproduction, because parameter coefficients are workedout after spreading RGB colors on the chromaticity diagram. In thistechnology, however, since the coefficients are not intuitivelyunderstandable, the parameters cannot be easily adjusted. Thistechnology is therefore hardly practical.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a color signalconverter that realizes, by means of intuitively-understandableparameters, the adjustment of colors represented by a signal after theconversion.

Another objective of the present invention is to provide a color displayapparatus that can reproduce an image with a sufficient brightness evenif the brightness of pixels is insufficient.

A color signal conversion apparatus of the present invention, whichconverts a three-primary-color signal to an n-color signal (n≧4),comprises: a first color signal generation module for generating, bysubjecting the three-primary-color signal to isochromatic conversion, anm-color signal made up of m color components (m≧n) including respectivecolor components that are equivalent in terms of color to colorcomponents of the n-color signal; and a second color signal generationmodule for generating the color components of the n-color signal, byperforming linear combination of the color components of the m-colorsignal.

A color signal conversion method of the present invention, forconverting a three-primary-color signal to an n-color signal (n≧4),comprises the steps of: generating, by subjecting thethree-primary-color signal to isochromatic conversion, an m-color signalmade up of m color components (m≧n) including respective colorcomponents that are equivalent in terms of color to color components ofthe n-color signal; and generating the color components of the n-colorsignal, by performing linear combination of the color components of them-color signal.

According to the above-described arrangement and method, athree-primary-color signal that is an original signal is subjected toisochromatic conversion, generating an m-color signal made up of m colorcomponents (m≧n) which are equivalent in terms of color with colorcomponents of a targeted n-color signal. The isochromatic conversion isperformed in such a manner that a combination of color componentsrepresenting a particular color is converted to a combination of othercolor components, without changing the represented color. The colorcomponents having equivalent colors are two color components whosepositions on a chromaticity diagram are relatively close to each otherand which are sensed as similar colors. The color components havingequivalent colors include two identical color components whose positionson the chromaticity diagram are identical with each other.

According to the above-described arrangement and method, furthermore,the color components of the n-color signal generated as a result of theconversion are generated by the linear combination of the colorcomponents of the m-color signal generated as above. The linearcombination of the color components is performed in such a manner thatmultiplication of coefficients and addition are performed with respectto each color component.

When the color components of the n-color signal are generated by thelinear combination of the color components of the m-color signal,intuitively-understandable parameters are used for adjusting the colorsrepresented by the n-color signal, and the coefficients of the linearcombination are determined by simple calculations of these parameters(see Tables. 1-8). As the parameters, it is possible to adopt, forinstance, values (cf. Tables 2, 4, and 6) indicating hue, colorsaturation, and brightness of each color component of the m-color signalor n-color signal and the values (cf. Table. 8) that indicate, in aneutral color between the color components, which one of the colorcomponents is enhanced.

In this manner, the above-described arrangement and method makes itpossible to perform the adjustment of colors represented by the n-colorsignal after the conversion, by means of intuitively-understandableparameters.

A display unit of the present invention includes one of the foregoingcolor signal conversion apparatuses and a display panel having n-colorpixels corresponding to the color components of the n-color signal.

According to this arrangement, it is possible to realize a display unitin which displayed colors can be adjusted usingintuitively-understandable parameters.

A color signal conversion program of the present invention realizes, bya computer, one of the foregoing color signal conversion apparatuses.This color signal conversion program can be implemented as a program forcausing a computer to operate as the aforesaid module. Acomputer-readable storage medium of the present invention can store theaforesaid color signal conversion program.

A color display apparatus of the present invention, for displaying acolor image, comprises: n-color pixels corresponding to n colorcomponents (n≧4) of which the color image is made up, wherein, said ncolor components include a first color component, a second colorcomponent, and a third color component obtained by performing colormixing of the first and second color components, and in a case where thethird equivalent color component of the m-color signal is reproduced bythe display panel, auxiliary illumination by means of pixelscorresponding to the first and second color components is performed inorder to enhance illumination by a pixel corresponding to the thirdcolor component.

A color display method for displaying a color image is arranged in sucha manner that n-color pixels corresponding to n color components (n≧4)of which the color image is made up is used, said n color componentsinclude a first color component, a second color component, and a thirdcolor component obtained by performing color mixing of the first andsecond color components, and in a case where the third equivalent colorcomponent of the m-color signal is reproduced, auxiliary illumination bymeans of pixels corresponding to the first and second color componentsis performed in order to enhance illumination by a pixel correspondingto the third color component.

According to the above-described arrangement and method, the pixelscorresponding to the first and second color components perform theauxiliary illumination, so that the third component is obtained as aresult of the color mixing, and the illumination of the pixelcorresponding to the third color component is enhanced. With this, evenwhen the brightness of the pixel corresponding to the third colorcomponent is insufficient, the third color component is reproduced witha sufficient brightness.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a color display apparatus ofEmbodiment 1 of the present invention.

FIG. 2 is a block diagram showing a color conversion circuit of thecolor display apparatus of FIG. 1.

FIG. 3 is a graph for illustrating the relationship between gray scalelevels of three primary colors and other color components.

FIG. 4 is a chromaticity diagram regarding the color display apparatusof FIG. 1, showing the relationship between the color range expected inthe input video signal and the color range that is displayable by amulticolor display panel.

FIG. 5 is a chromaticity diagram regarding the color display apparatusof FIG. 1, showing the relationship between the color range expected inthe input video signal and the color range displayable by a multicolordisplay panel, in a case where these color ranges are matched with eachother.

FIG. 6 is a chromaticity diagram regarding the color display apparatusof FIG. 1, for illustrating a method of adjusting the differences of hueand color saturation, between the color range expected in the inputvideo signal and the color range that is displayable by a multicolordisplay panel.

FIG. 7 is a block diagram showing a color display apparatus ofEmbodiment 2 of the present invention.

FIG. 8 is a block diagram showing a color conversion circuit of thecolor display apparatus of FIG. 7.

FIG. 9 is a chromaticity diagram regarding the color display apparatusof FIG. 7, showing the relationship between the color range expected inthe input video signal and the color range that is displayable by amulticolor display panel.

FIG. 10 is a block diagram showing a color display apparatus ofEmbodiment 3 of the present invention.

FIG. 11 is a block diagram of a color conversion circuit of the colordisplay apparatus of FIG. 10.

FIG. 12 is a graph for illustrating the relationship between gray levelsof three primary colors and other color components.

FIG. 13 is a graph for illustrating the relationship between said othercolor components and a further color component.

FIG. 14 illustrates color adjustment of neutral colors.

FIG. 15 is a graph showing an example of a function used as matrixcoefficients.

FIG. 16 is a chromaticity diagram showing the relationship between achromaticity point as a result of additive color mixing of R and Gpixels and a chromaticity point of a Y pixel.

FIG. 17 is a graph showing an example of functions used as matrixcoefficients.

FIG. 18 is a graph showing an example of functions used as matrixcoefficients.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

The following will describe Embodiment 1 of the present invention inreference to FIGS. 1-6.

(Preconditions)

In the present embodiment, an input video signal is made up of R, G, andB primary-color signals with X gray levels (black (0) to white (X-1)).That is to say, the input video signal is a 3x-bit color digital videosignal made up of: an x-bit digital signal R with X gray levels (X=2x),which represents a red gray level by an integer (gray level value) r inthe range of 0 to (X-1); an x-bit digital color signal G with X graylevels (X=2x), which represents a green gray level by an integer g inthe range of 0 to (X-1); and an x-bit digital signal B with X graylevels, which represents a blue gray level by an integer (gray levelvalue) b in the range of 0 to (X-1).

The video signal of the present embodiment may represent a moving imageor a static image.

In the present embodiment, the r, g, and b gray levels are divided by(2x-1) so as to be converted to standardized values that fall in therange of (0≦r, g, b≦1).

The above-described preconditions are applicable to Embodiments 2 and 3as well.

(Configuration of Apparatus)

As shown in FIG. 1, a color display apparatus 100 of the presentembodiment includes a multicolor display panel 101, a color conversioncircuit 102, and a control section 103.

The above-mentioned “multicolor display” indicates color imagereproduction realized by suitably mixing not less than four basicdisplay colors (basic colors). Also, “multicolor display panel” is adisplay panel that realizes the multicolor display by means of pixelscorresponding to the basic colors.

The present embodiment assumes that 5 basic colors are used in themulticolor display panel 101. In this respect, in the presentembodiment, the multicolor display panel 101 may be at times termed5-color display panel 101.

It is noted that any types of devices can be used as the multicolordisplay panel 101, on condition that the device can perform multicolordisplay. Examples of such devices include a liquid crystal displaypanel, a CRT, a PDP, and a liquid crystal projector.

A video signal supplied to the color display apparatus 100 is athree-primary-color signal representing R (red), G (green) and B (blue).This video signal is converted, by the color conversion circuit 102,into a video signal d1 through d5 used in the 5-color display panel 101,and the video signal d1 through d5 is supplied to the 5-color displaypanel 101.

In the color display apparatus 100, colors of an image displayed on the5-color display panel 101 can be adjusted. This adjustment is instructedby the user through the control section 103. The control section 103receives such an instruction, and supplies, to the color conversioncircuit 102, an adjustment signal corresponding to the instruction. Inaccordance with the adjustment signal supplied from the control section103, the color conversion circuit 102 adjusts the video signal. Thisadjustment of the video signal by the color conversion circuit 102 willbe specifically described later.

Although the present embodiment assumes that the video signal suppliedto the color display apparatus 100 represents three primary colors of R,G, and B, the video signal may represent another type of three primarycolors such as YMC (Yellow, Magenta, and Cyan). Moreover, the videosignal supplied to the color display apparatus 100 does not have torepresent the aforesaid primary colors. The video signal may be, forinstance, a signal that can be converted to three primary color signals,such as a YCrCb signal typically used as a color television signal. Insuch a case, an arrangement for converting the YCrCb signal to athree-primary color video signal is required.

FIG. 2 illustrates a block diagram of the color conversion circuit 102.The color conversion circuit 102 includes an inverse gamma correctionsection 11, a color component extraction section 12, a matrix operationsection 13, a clipping section 14, a gamma correction section 15, and amatrix generation section 16.

The inverse gamma correction section 11 performs inverse gammacorrection on a video signal PS0 supplied to the color conversioncircuit 102. The present embodiment assumes such a case that the videosignal PS0 is supplied to the color conversion circuit 102, after beingsubjected to gamma correction. In the video signal having been subjectedto the gamma correction, the relationship between the gray level and thebrightness is nonlinear. On this account, the inverse gamma correctionsection 11 performs the inverse gamma correction, so as to cause therelationship between the gray level and the brightness to be linear.

In this manner, it is preferable that the inverse gamma correction beperformed on the video signal PS0 supplied to the color conversioncircuit 102, in a case where the video signal PS0 has been subjected tothe gamma correction. However, in some cases, subsequent processes aresuccessfully carried out even if the video signal having been subjectedto the gamma correction is used without performing the inverse gammacorrection thereon. If so, the inverse gamma correction section 11 canbe omitted. The inverse gamma correction section 11 can also be omittedwhen the video signal PS0 supplied to the color conversion circuit 102is not subjected to the gamma correction.

The color component extraction section 12 classifies a video signal PS1into six patterns based on the magnitude relation of R, G, and B graylevels of the video signal PS1 after being subjected to the inversegamma correction by the inverse gamma correction section 11, and thenthe color component extraction section 12 performs an operationcorresponding to the pattern. As a result, the color componentextraction section 12 generates a video signal PS2 representing colorcomponents of red (ro), green (go), blue (bo), yellow (yo), magenta(mo), cyan (co), and white (wo), by performing a calculationcorresponding to each pattern.

The matrix operation section 13 performs a matrix operationcorresponding to the number of basic colors of the 5-color display panel101, so as to reorganize the color components of the video signal PS2into the color components d1 through d5 corresponding to the basiccolors of the 5-color display panel 101. As a result, the matrixoperation section 13 generates a five-color video signal PS3.

The clipping section 14 generates a video signal PS4 by subjecting thevideo signal PS3 to clipping. This clipping is such a process that agray level exceeding the upper allowable limit (1) or being lower thanthe lower allowable limit (0) is caused to fall within an allowablerange.

The gamma correction section 15 performs, on the video signal PS4, gammacorrection in accordance with the gamma characteristics of the 5-colordisplay panel 101, so as to generate a video signal PS5. This videosignal PS5 is supplied to the 5-color display panel 101.

Based on an adjustment signal supplied from the control section 103, thematrix generation section 16 generates a matrix used for the matrixoperation performed by the matrix operation section 13, and the matrixgeneration section 16 supplies the generated matrix to the matrixoperation section 13. This matrix generated by the matrix generationsection 16 will be specifically described later.

(Processes)

Now, the following specifically describes the processes performed by thecolor component extraction section 12, the matrix operation section 13,and the matrix generation section 16.

When the video signal PS1 is supplied to the color component extractionsection 12, the magnitude relation of gray levels r, g, and b of therespective color signals is evaluated. That is, it is determined towhich one of the following six patterns the values of r, g, and b of thevideo signal fit:r>g>b   [1]r>b>g   [2]b>r>g   [3]b>g>r   [4]g>b>r   [5]g>r>b   [6]

Note that, the above-described patterns [1]-[6] do not include an equalsign. In reality, equal signs are suitably added in such a manner as toallow each of the combinations of r, g, and b to be included in only oneof the patterns [1]-[6]. In the present case, equal signs are set asfollows:r≧g≧b   [1]r≧b≧g   [2]b>r≧g   [3]b>g>r   [4]g≧b>r   [5]g>r≧b   [6]

It is noted that equal signs may be differently set on condition thatthe relationship between the equal signs does not contradict each other.

The color component extraction section 12 extracts the gray levels ro,go, bo, yo, mo, co, and wo of red, green, blue, yellow, magenta, cyan,and white, in the following manner:

[1] Provided that r≧g≧b,ro=(r−g)yo=(g−b)go=bo=mo=co=0wo=b[2] Provided that r≧b>g,ro=(r−g)mo=(b−g)go=bo=yo=co=0wo=g

[3] Provided that b>r≧g,bo=(b−r)mo=(r−g)ro=go=yo=co=0wo=g

[4] provided that b>g>r,bo=(b−g)co=(g−r)ro=go=yo=mo=0wo=r

[5] Provided that g≧b>r,go=(g−b)co=(b−r)ro=bo=yo=mo=0wo=r

[6] Provided that g>r≧b,go=(g−r)yo=(r−b)ro=bo=mo=co=0wo=b

In reference to FIG. 3, the meaning of the above-described calculationsby the color component extraction section 12 will be discussed.

FIG. 3 illustrates a case where the magnitude relation of the graylevels r, g, and b of the video signal PS1 fit into the pattern [1]. Inthe vertical direction of FIG. 3, these gray levels r, g, and b can bedivided as shown in the figure.

First, all of the gray levels r, g, and b have white components. Forthis reason, in the case of FIG. 3, a gray level corresponding to thegray level b is wo. In a similar manner, in the case of FIG. 3, sincethe gray levels g and b have yellow components, a gray levelcorresponding to a difference between g and b is yo. Also, in the caseof FIG. 3, a difference between r and g corresponds to a gray level ro.

In the case of r>g>b, since there are no color components correspondingto go, bo, mo, and co, the gray levels of these color components are 0.

As to the patterns [2]-[6], the conversion of color components can becarried out in a similar manner as that of the pattern [1]. As to eachof the patterns [1]-[6], therefore, the color components ro, go, bo, yo,mo, co, and wo are worked out by the aforesaid calculations.

The matrix operation section 13 works out the following equation (1)using the color components ro, go, bo, yo, mo, co, and wo worked out bythe color component extraction section 12, so as to generate the videosignal PS3 made up of the color components d1 through d5.

[Equation (1)] $\begin{matrix}{\begin{pmatrix}{d1} \\{d2} \\\vdots \\{d5}\end{pmatrix} = {A_{5 \times 7}\begin{pmatrix}{ro} \\{go} \\{bo} \\{yo} \\{mo} \\{co} \\{wo}\end{pmatrix}}} & (1)\end{matrix}$

In the equation (1), A_(5×7) is a 5×7 matrix and represented by anequation (2) as follows: $\begin{matrix}\text{[Equation~~(2)]} & \quad \\{A_{5 \times 7} = \begin{pmatrix}a_{11} & a_{12} & a_{13} & a_{14} & a_{15} & a_{16} & a_{17} \\a_{21} & a_{22} & a_{23} & a_{24} & a_{25} & a_{26} & a_{27} \\a_{31} & a_{32} & a_{33} & a_{34} & a_{35} & a_{36} & a_{37} \\a_{41} & a_{42} & a_{43} & a_{44} & a_{45} & a_{46} & a_{47} \\a_{51} & a_{52} & a_{53} & a_{54} & a_{55} & a_{56} & a_{57}\end{pmatrix}} & (2)\end{matrix}$

In the equation (2), elements (matrix coefficients) a_(ij) in the matrixA_(5×7) are determined in line with the basic colors of the 5-colordisplay panel 101, and are adjusted in line with the adjustment signal.These matrix coefficients are determined by the matrix generationsection 16. The following will discuss how the matrix coefficients aredetermined.

FIG. 4 illustrates the basic colors of the 5-color display panel 101, aspoints d1 through d5 on a chromaticity diagram. These basic colorscorrespond to d1 through d5. FIG. 4 also represents primary colorsexpected in the video signal PS1, as points R, G, and B on thechromaticity diagram, and further illustrates points Y, M, C, and W onthe chromaticity diagram, which correspond to yellow, magenta, cyan, andwhite worked out from the points R, G, and B. The points Y, M, C, and Won the chromaticity diagram meet (r=g, b=0), (r=b, g=0), (g=b, r=0), and(r=g=b), respectively.

It is noted that the present embodiment assumes that five basic colorsof the 5-color display panel 101 are red (D1), green (D2), blue (D3),yellow (D4), and cyan (D5).

In general, a multicolor display panel is advantageous in that a widercolor reproduction range is realized as compared to athree-primary-color display panel. On this account, the colorreproduction range of the multicolor display panel is often designed soas to be wider than a color reproduction range estimated in athree-primary-color input signal (video signal PS0 or PS1). In thisregard, as shown in FIG. 4, on a chromaticity diagram, the points of thethree primary colors represented by the input signal are oftenpositionally different from the points of the basic colors of themulticolor display panel. As a result, in some cases colors of an imagedisplayed on the multicolor display panel are inappropriate orinsufficient, if three primary colors represented by the input signalare simply converted to basic colors of the multicolor display panel.

To solve this problem, in the present embodiment a video signal isadjusted using an adjustment signal. More specifically, this adjustmentis realized by adjusting matrix coefficients.

For purposes of illustration, it is assumed that the relationshipbetween the points of three primary colors of the input signal and thepoints of the basic colors of the multicolor display panel is as shownin FIG. 5, i.e., on a chromaticity diagram, the points R, G, B, Y, and Care in the same positions as the points D1, D2, D3, D4, and D5, and thecorresponding points have an identical brightness.

In this case, the matrix coefficients are set as in an equation (3).$\begin{matrix}\text{[Equation~~3]} & \quad \\{A_{5 \times 7} = \begin{pmatrix}1 & 0 & 0 & 0 & 1 & 0 & 1 \\0 & 1 & 0 & 0 & 0 & 0 & 1 \\0 & 0 & 1 & 0 & 1 & 0 & 1 \\0 & 0 & 0 & 1 & 0 & 0 & 1 \\0 & 0 & 0 & 0 & 0 & 1 & 1\end{pmatrix}} & (3)\end{matrix}$

The equation (1) is expanded using the equation (3), so that thefollowing equations are obtained:d 1=ro+mo+wod 2=go+wod 3=bo+mo+wod 4=yo+wod 5=co+wo

As the equations as a result of the expansion show, a 5-color videosignal PS3 is obtained by (i) distributing, to d1 through d5, thecorresponding color components, (ii) commonly adding the white componentto all of d1 through d5, and (iii) evenly adding the color component moto d1 and d3. The color component mo is evenly added to d1 and d3,because of the following reason: since the 5-color display panel 101does not support a basic color point corresponding to magenta, thecomponent mo is represented by D1 and D3. As a result of theabove-described calculations, the video signal PS3 representing d1through d5 is generated.

However, as shown in FIG. 4, the actual points D1 through D5 of thebasic colors of the 5-color display panel 101 are not matched with thepoints R, G, B, Y, M, C, and W that are expected in the input signal.For this reason, the matrix coefficients of the equation (3) arepreferably adjusted.

For instance, it is assumed that the relationship between Y and D4 is asshown in FIG. 6. FIG. 6 is a close-up of a part around Y in FIG. 4.When, as FIG. 6 shows, D4 is on the R side with respect to a lineconnecting W and Y, the color reproduced at d4 (=yo+wo) is reddishyellow as compared to thee yellow color expected in the input signal.

To adjust this difference between the hues, d4 is allocated to yo, avalue worked out by multiplying yo by a predetermined coefficient isadded to the equation for calculating d2, and a value worked out bymultiplying yo by a predetermined coefficient is subtracted from theequation for calculating d1. In other words, the yellow hue can beadjusted by changing the coefficients a₁₄ and a₂₄.

In the meanwhile, when, as shown in FIG. 6, D4 is on the outside of theline connecting W and Y, i.e. D4 is on the opposite side to W, thereproduced color has a color saturation (color purity) higher than thatof the yellow color expected in the input signal.

To adjust this difference in color saturation, a value worked out bymultiplying yo by a predetermined coefficient is added to each of theequations for calculating d1, d2, d3, and d5. In this case, thebrightness levels of d1, d2, d3, and d5 increase. Therefore, tocompensate the increase of the overall brightness level, the coefficientby which yo is multiplied may be decreased in the equation forcalculating d4. That is to say, to adjust the color saturation of theyellow color, the coefficients a₁₄, a₂₄, a₃₄, and a₅₄ are adjusted, andthe coefficient a₄₄ is further adjusted in order to compensate thechange of the overall brightness as a result of the adjustment of thecoefficients a₁₄, a₂₄, a₃₄, and a₅₄.

When the brightness of D4 is higher than the brightness of Y, thebrightness of the reproduced yellow color is brighter than thebrightness expected in the input signal.

To adjust this difference in brightness, a coefficient of y1 in theequation for calculating d4 is decreased. In other words, the brightnessof the yellow color can be adjusted by adjusting the coefficient a₄₄.

Although the description above relates to the yellow color, the hue,color saturation, and brightness of other colors can be adjusted in asimilar manner. Table. 1 illustrates a concrete example of the matrixcoefficients for the adjustments of these parameters. It is noted thatthe adjusting parameters (the hue, color saturation, and brightness) aredefined as shown in Table. 2. TABLE 1 a₁₁ = Vr − Sr a₁₂ = ½.Sg a₁₃ = −Hba₂₁ = 0 a₂₂ = Vg − Sg a₂₃ = 0 a₃₁ = +Hr a₃₂ = ½.Sg a₃₃ = Vb − Sb a₄₁ =−Hr a₄₂ = +Hg a₄₃ = +Sb a₅₁ = +SR a₅₂ = −Hg a₅₃ = +Hb a₁₄ = Hy a₁₅ = 1a₁₆ = Sc a₂₄ = −Hy a₂₅ = 0 a₂₆ = +Hc a₃₄ = Sy a₃₅ = 1 a₃₆ = −Hc a₄₄ = Vy− Sy a₄₅ = 0 a₄₆ = 0 a₅₄ = 0 a₅₅ = 0 a₅₆ = Vc − Sc a₁₇ = 1 a₂₇ = 1 a₃₇ =1 a₄₇ = 1 a₅₇ = 1

TABLE 2 COLOR HUE SATULATION BRIGHTNESS RED Hr Sr Vr GREEN Hg Sg Vg BLUEHb Sb Vb YELLOW Hy Sy Vy CYAN Hc Sc Vc

These adjusting parameters in Table. 2 are integers. When the adjustingparameter of the hue has a positive/negative value, the hue is adjustedclockwise/counterclockwise on the chromaticity diagram. When theadjusting parameter of the color saturation is a positive/negativevalue, the color saturation is adjusted so as to decrease/increase onthe chromaticity diagram. Also, when the adjusting parameter of thebrightness is not less than 1 or not more than 1, the brightness isadjusted so as to increase or decrease.

In the present case, the adjusting parameters are integers, in order tocause the gray levels d1 through d5 to be integers. The adjustingparameters, however, are not necessarily integers, when the video signalPS3 is not necessarily an integer or when, after calculating d1=d5, theresults of the calculations of d1 and d5 are rounded to integers.

The above-described method of adjusting the matrix coefficients is onlyan example. The adjustment may be performed in a different manner.

For instance, apart from the aforesaid method in which Sr is added toa₅₁ while Sr is subtracted from all, the adjustment of color saturationof red color may be performed in such a manner that Sr is added to a₂₁and a₂₃ and then Sr is subtracted from a₁₁.

In the above-described example, moreover, the operation of adding Sr toa₅₁ and subtracting Sr from a₁₁ is performed for keeping averagebrightness. This operation presumes that D1 and D5 in FIG. 4 have anidentical brightness. If D1 and D5 have different brightness, each Sr ispreferably multiplied by a correction coefficient that takes thedifference of brightness into account.

Moreover, in the chromaticity diagram, a primary color expected in theinput signal is not necessarily matched with a basic color of the5-color display panel 101, as long as the color is adjusted so as not tolook inappropriate. In some cases, the color saturation and brightnessare enhanced for the sake of a better display quality, even if the colorsaturation and brightness are not matched with original values. Also inthis case, the matrix coefficients are adjusted in such a manner as toobtain a desirable display quality.

When the matrix coefficients have certain values, d1 through d5generated by the matrix operation section 13 may be more than 1 or lessthan 0. In such a case, the clipping is carried out by the clippingsection 14, so that d1 through d5 are caused to fall within the range of0≦d1, d2, d3, d4, d5≦1.

Also, since the 5-color display panel 101 has gamma characteristics, thegamma correction section 15 performs the gamma correction on the videosignal PS4 after being subjected to the clipping.

As described above, the color conversion circuit 102 is a color signalconverter that converts a three-primary-color signal to a 5-colorsignal. Since the present embodiment assumes that the multicolor displaypanel 101 has a 5-color pixel, the color conversion circuit 102 performsthe conversion to 5-color signals. In the present invention, however,the multicolor display panel 101 may be a display panel having n-colorpixels corresponding to n colors (n≧4). In such a case, the colorconversion circuit 102 performs the conversion to an n-color signalrepresenting that number of the colors.

The color conversion circuit 102 includes the color component extractionsection 12 serving as a first color signal generation module thatgenerates, by subjecting the three-primary-color signal to isochromaticconversion, an m-color signal made up of m color components (m≧n)including colors equivalent to those of the color components of then-color signal. It is noted that the color components having equivalentcolors are two color components whose positions on the chromaticitydiagram are relatively close to each other and which are sensed assimilar colors, such as R and D1, G and D2, B and D3, Y and D4, and Cand D5 in FIG. 4.

The color conversion circuit 102 also includes the matrix operationsection 13 serving as a second color signal generation module thatgenerates the color components of the n-color signal by performinglinear combination of the color components of the m-color signal. Thelinear combination of the color components indicates that, as shown inthe equation (1), the sum total of color components each multiplied by acoefficient.

The generation of the color components of the n-color signal, which isperformed by the linear combination of the color components of them-color signal, is carried out in the following manner.

Since the color components of the m-color signal include colorcomponents whose colors are equivalent to the colors of the colorcomponents of the n-color signal, these color components having theequivalent colors can be allocated as the corresponding color componentsof the n-color signal. If the color components of the m-color signalincludes those not corresponding to the color components of the n-colorsignal (i.e. some color components are redundant), these redundant colorcomponents are suitably allocated to the color components of the n-colorsignal. This allocation is realized by changing the matrix coefficientsin the equation (1) to those in the equation (3).

Furthermore, the aforesaid allocation is adjusted using, as parameters,the hue, color saturation, and brightness regarding the color componentsof the n-color signal. With this, the colors represented by the n-colorsignal can be adjusted in accordance with these parameters. Thisadjustment is realized by setting the matrix coefficients in theequation (1) in line with Table. 1.

In this manner, in the color conversion circuit 102, the adjustment ofthe colors represented by the n-color signal can be performed using, asthe parameters, the hue, color saturation, and brightness regarding thecolor components of the n-color signal. The hue, color saturation, andbrightness regarding the color components of the n-color signal areintuitively understandable. On this account, the color conversioncircuit 102 is capable of adjusting the colors represented by theconverted signal, using intuitively-understandable parameters.

Incidentally, the color component extraction section 12 sets thefollowings as the m color components: primary-color components of thethree-primary-color signal; complementary color components correspondingto the respective primary-color components; and an achromatic-colorcomponent. With this, as the above-described patterns [1]-[6] show, them-color signal is generated by performing simple calculations such assubtracting one primary-color component from another primary-colorcomponent.

The color conversion circuit 102 is further provided with the matrixgeneration section 16 serving as a coefficient change module forchanging the matrix coefficients used in the matrix operation section13. The color conversion circuit 102, however, is not necessarilyprovided with the matrix generation section 16. In such a case, theaforesaid adjustment may be performed at the time of manufacture of thecolor conversion circuit 102, by an adjusting device equivalent to thematrix generation section 16 and the control section 103. Even so,incorporating the matrix generation section 16 into the color conversioncircuit 102 and providing the control section 103 are advantageous inthat the adjustment can be performed at any time, even after theshipment of the color display apparatus 100.

The characteristic feature of the color conversion circuit 102 can berephrased as follows: the color conversion circuit 102 is a signalconverter that converts a three-dimensional video signal to ann-dimensional video signal supplied to the multicolor display panel 101including n-color (n≧4) pixels. The color conversion circuit 102 (i)identifies which one of six patterns categorized in accordance with themagnitude relation of gray levels of the three-dimensional video signalis matched with the pattern of the actually-inputted three-dimensionalvideo signal, (ii) extracts a plurality of color components byperforming an operation corresponding to each pattern, and (iii)reorganizes the extracted color components into the input signal to themulticolor display panel 101. Furthermore, the color conversion circuit102 generates a multi-dimensional video signal, using (I) a first modulethat extracts red (ro), green (go), blue (bo), yellow (yo), cyan (co),magenta (mo), and white (wo) components, by identifying 6 patterns fromthe gray levels of the three-dimensional video signal and performing anoperation corresponding to each pattern and (II) a second module thatreorganizes these components, by means of the aforesaid matrix operationin line with n.

With this color conversion circuit 102, a multi-dimensional video signalcorresponding to a multicolor display apparatus is generated byperforming an operation based on a typically-used three-dimensionalvideo signal.

It is noted that the matrix coefficients in the equation (2) may bechanged in accordance with the result of the identification of thepatterns by the color component extraction section 12.

Also, the components ro, go, bo, yo, mo, co, and wo may be subjected tothe matrix operation by the matrix operation section 13, after beingsubjected to nonlinear processing.

Embodiment 2

The following will describe Embodiment 2 of the present invention, inreference to FIGS. 7-9.

As shown in FIG. 7, a color display apparatus 200 of the presentembodiment includes a multicolor display panel 201, a color conversioncircuit 202, and a control section 103.

The multicolor display panel 201 of the present embodiment is differentfrom the 5-color display panel 101 of Embodiment 1. The multicolordisplay panel 201 supports four basic colors (R, G, and B primary colorsand white). In this regard, in the present embodiment, the multicolordisplay panel 201 may be at times termed 4-color display panel 201.

As shown in FIG. 8, the color conversion circuit 202 of the presentembodiment is different from the color conversion circuit 102 ofEmbodiment 1. The color conversion circuit 202 is a processing circuitcorresponding to the multicolor display panel 201 and has a blockconfiguration similar to that of the color conversion circuit 102 ofEmbodiment 1 (shown in FIG. 2). The color conversion circuit 202 isdifferent from the color conversion circuit 102 in that the colorconversion circuit 202 is provided with a matrix operation section 23and a matrix generation section 26 that perform operations differentfrom those by he matrix operation section 13 and the matrix generationsection 16. These circuits are also different in that, in the colorconversion circuit 202, each of the video signals PS3-PS5 are made up ofd1 through d4.

Apart from the above, the control section 103 and the color conversioncircuit 202 have the same functions as those described in Embodiment 1,so that the same numbers are given and the descriptions are omitted forthe sake of convenience.

In FIG. 9, (i) basic colors of the 4-color display panel 201, whichrespectively correspond to d1 through d4, are represented as points D1through D4 on a chromaticity diagram, (ii) primary colors expected in avideo signal PS1 are represented as points R, G, and B on thechromaticity diagram, and (iii) yellow, magenta, cyan, and white, whichare worked out from the points R, G, and B, are represented as points Y,M, C, and W on the chromaticity diagram. As shown in FIG. 9, the pointD4, which corresponds to white that is one of the basic colors of themulticolor display panel 201, locates inside a chromaticity area formedby the points D1 through D3.

A matrix operation section 23 of the color conversion circuit 202 worksout an equation (4) using the components ro, go, bo, yo, mo, co, and wocalculated by the color component extraction section 12 in a mannersimilar to those of Embodiment 1. As a result, the matrix operationsection 23 generates a video signal PS3 made up of d1 through d4.$\begin{matrix}\text{[Equation~~~4]} & \quad \\{\begin{pmatrix}{d1} \\{d2} \\{d3} \\{d4}\end{pmatrix} = {A_{4 \times 7}\begin{pmatrix}{ro} \\{go} \\{bo} \\{yo} \\{mo} \\{co} \\{wo}\end{pmatrix}}} & (4)\end{matrix}$

In the equation 4, A_(4×7) is a 4×7 matrix and represented by anequation (5) as follows: $\begin{matrix}\text{[Equation~~5]} & \quad \\{A_{4 \times 7} = \begin{pmatrix}a_{11} & a_{12} & a_{13} & a_{14} & a_{15} & a_{16} & a_{17} \\a_{21} & a_{22} & a_{23} & a_{24} & a_{25} & a_{26} & a_{27} \\a_{31} & a_{32} & a_{33} & a_{34} & a_{35} & a_{36} & a_{37} \\a_{41} & a_{42} & a_{43} & a_{44} & a_{45} & a_{46} & a_{47}\end{pmatrix}} & (5)\end{matrix}$

Elements (matrix coefficients) a_(ij) of the matrix A_(4×7) aredetermined in accordance with the basic colors of the 4-color displaypanel 201, and are adjusted in accordance with an adjustment signal. Thematrix coefficients are set by the matrix generation section 26, inaccordance with Table. 3 in a similar manner as in Embodiment 1. It isnoted that the adjusting parameters (hue, color saturation, andbrightness) are defined as shown in Table 4. In this case, it is assumedthat white color corresponding to d4 is not necessarily adjusted. TABLE3 a₁₁ = Vr − Sr a₁₂ = +Hg a₁₃ = −Hb a₂₁ = −Hr a₂₂ = Vg − Sg a₂₃ = +Hba₃₁ = +Hr a₃₂ = −Hg a₃₃ = Vb − Sb a₄₁ = 0 a₄₂ = 0 a₄₃ = 0 a₁₄ = 1 a₁₅ =1 a₁₆ = 0 a₂₄ = 1 a₂₅ = 0 a₂₆ = 1 a₃₄ = 0 a₃₅ = 1 a₃₆ = 1 a₄₄ = 0 a₄₅ =0 a₄₆ = 0 a₁₇ = 1 a₂₇ = 1 a₃₇ = 1 a₄₇ = 1

TABLE 4 COLOR HUE SATULATION BRIGHTNESS RED Hr Sr Vr GREEN Hg Sg Vg BLUEHb Sb Vb

As a matter of course, the aforesaid case is merely an example asdescribed in Embodiment 1.

By the way, the adjustment of the white color is realized by adjustingthe seventh column of the matrix coefficients. For instance, when whitecolor is yellowish as compared to the white color expected in the inputsignal, a coefficient a₃₇ is set so as to be larger than 1, orcoefficients a₁₇ and a₂₇ are set so as to be smaller than 1.Alternatively, in consideration of average brightness, the coefficienta₃₇ is set so as to be larger than 1, while the coefficients a₁₇ and a₂₇are set so as to be smaller than 1.

In this manner, the color conversion circuit 202 can generate a videosignal corresponding to the multicolor display panel 201 including“white” pixels. The color conversion circuit 202 can adjust the hue,color saturation, and brightness of d1 through d3.

As described above, the color conversion circuit 202 is a color signalconverter that converts a three-primary-color signal to a 4-color signalrepresenting colors including white. In the present embodiment, thecolor conversion circuit 202 performs conversion to the four-colorsignal because a display panel including four-color pixels is adopted asthe multicolor display panel 101. Alternatively, a display panelincluding n-color (n≧4) pixels may be adopted as the multicolor displaypanel 201. In this case, the color conversion circuit 202 performsconversion to a n-color signal corresponding to the number of the colorsof the pixels.

The color conversion circuit 202 includes the color component extractionsection 12 serving as a first color signal generation module thatgenerates, by subjecting the three-primary-color signal to isochromaticconversion, an m-color signal made up of m color components (m≧n)including colors equivalent to those of the color components of then-color signal. It is noted that the color components having equivalentcolors are two color components whose positions on a chromaticitydiagram are relatively close to each other and which are sensed assimilar colors, such as R and D1, G and D2, B and D3, and W and D4 inFIG. 9. Color components having equivalent colors include two identicalcolor components, such as W and D4, whose positions on the chromaticitydiagram are identical with each other.

With this, in a manner similar to Embodiment 1, the color conversioncircuit 202 makes it possible to adjust the colors represented by asignal after the conversion, by means of intuitively-understandableparameters.

As in Embodiment 1, the color conversion circuit 202 further includes amatrix generation section 26 serving as a coefficient change module thatchanges the matrix coefficients in the matrix operation section 23.

The characteristic feature of the color conversion circuit 202 can berephrased as follows: the color conversion circuit 202 is a signalconverter that converts a three-dimensional video signal to ann-dimensional video signal supplied to the multicolor display panel 201including n-color (n≧4) pixels. The color conversion circuit 202 (i)identifies which one of six patterns categorized in accordance with themagnitude relation of gray levels of the three-dimensional video signalis matched with the pattern of the actually-inputted three-dimensionalvideo signal, (ii) extracts a plurality of color components byperforming an operation corresponding to each pattern, and (iii)reorganizes the extracted color components into the input signal to themulticolor display panel 201. Furthermore, the color conversion circuit202 generates a multi-dimensional video signal, using (I) a first modulethat extracts red (ro), green (go), blue (bo), yellow (yo), cyan (co),magenta (mo), and white (wo) components, by identifying 6 patterns fromthe gray levels of the three-dimensional video signal and performing anoperation corresponding to each pattern and (II) a second module thatreorganizes these components, by means of the aforesaid matrix operationin line with n.

With this color conversion circuit 202, a multi-dimensional video signalcorresponding to a multicolor display apparatus is generated byperforming an operation based on a typically-used three-dimensionalvideo signal.

It is noted that the matrix coefficients in the equation (5) may bechanged in accordance with the result of the identification of thepatterns by the color component extraction section 12.

Also, the components ro, go, bo, yo, mo, co, and wo worked out by thecolor component extraction section 12 may be subjected to the matrixoperation by the matrix operation section 23, after being subjected tononlinear processing.

Embodiment 3

The following will describe Embodiment 3 of the present invention inreference to FIGS. 10-13.

As shown in FIG. 10, a color display apparatus 300 of the presentembodiment includes a multicolor display panel 101, a color conversioncircuit 302, and a control section 103.

The color conversion circuit 302 of the present embodiment is differentfrom the color conversion circuit 102 of Embodiment 1. The controlsection 103 and the 5-color display panel 101 are more or less identicalwith those in Embodiment 1, so that these members are given the samenumbers and the descriptions thereof are omitted for the sake ofconvenience.

As shown in FIG. 11, the color conversion circuit 302 is different fromthe color conversion circuit 102 in that, primarily, the colorconversion circuit 302 is provided with a color component extractionsection 32, a matrix operation section 33, and a matrix generationsection 36, which perform processes different from those performed bythe color component extraction section 12, the matrix operation section13, and the matrix generation section 16. The difference between thesecircuits is also in that, in addition to signals representing respectivecolor components of red (ro), green (go), blue (bo), yellow (yo),magenta (mo, cyan (Co), and white (wo) a video signal PS2 in the colorconversion circuit 302 includes signals representing neutral colors(described later).

Apart from the above, the arrangement of the color conversion circuit302 are more or less identical with those in Embodiment 1 so that sucharrangements are given the same numbers and the descriptions thereof areomitted for the sake of convenience.

The color component extraction section 32 generates a video signal PS2representing 13 types of color components (in addition to red (ro),green (go), blue (bo), yellow (yo), magenta (mo), cyan (co), and white(wo), there are red-yellow (ry), red-magenta (rm), blue-magenta (bm),blue-cyan (bc), green-cyan (gc), and green-yellow (gy) that are neutralcolors between the colors ro through co), by the following operation:(i) a video signal PS1 after being subjected to inverse gamma correctionby the inverse gamma correction section 11 is classified into sixpatterns, in accordance with the magnitude relation of R, G, and B graylevels of the video signal PS1, (ii) these patterns are furtherclassified into two sub-patterns, and (iii) an operation correspondingto each pattern and sub-pattern is performed.

More specifically, when the video signal PS1 is supplied to the colorcomponent extraction section 12, it is determined which one of thefollowing six patterns the values r, g, and b of the video signal fitinto. The video signal is supplied in a manner similar to Embodiment 1.r≧g≧b   [1]r≧b>g   [2]b>r≧g   [3]b>g>r   [4]g≧b>r   [5]g>r≧b   [6]

Then the gray levels the aforesaid 13 types of color components ro, go,bo, yo, mo, co, wo, ry, rm, bm, bc, gc, and gy are worked out in thefollowing manners:

[1] In a case where r≧g≧b,ro=(r−g)yo=(g−b)wo=bgo=bo=mo=co=0

-   -   <1> if ro≧yo, ry=yo    -   <2> if ro<yo, ry=ro        gy=gc=bc=bm=rm=0

[2] In a case where r≧b>g,ro=(r−b)mo=(b−g)wo=ggo=bo=yo=co=0

-   -   <3> if ro≧mo, rm=mo    -   <4> if ro<yo, rm=ro        ry=gy=gc=bc=bm=0

[3] In a case where b>r≧g,bo=(b−r)mo=(r−g)wo=gro=go=yo=co=0

-   -   <5> if bo≧mo, bm=mo    -   <6> of bo<mo, bm=bo        ry=gy=gc=bc=rm=0

[4] In a case where b>g>r,bo=(b−g)co=(g−r)wo=rro=go=yo=mo=0

-   -   <7> if bo≧co, bc=co    -   <8> if bo<co, bc=bo        ry=gy=gc=bm=rm=0

[5] In a case where g≧b>r,go=(g−b)co=(b−r)wo=rro=bo=yo=mo=0

-   -   <9>if go≧co, gc=co    -   <10>if go<co, gc=co        ry=gy=bc=bm=rm=0

[6] In a case where g>r≧b,go=(g−r)yo=(r−b)wo=bro=bo=mo=co=0

-   -   <11> if go≧yo, gy=yo    -   <12>if go<yo, gy=go        ry=gc=bc=bm=rm=0

Referring to FIGS. 12 and 13, the meaning of these calculationsperformed in the color component extraction section 32 will bedescribed.

In the above-described calculations, the magnitude relation of theextracted ro, go, bo, yo, mo, co, and wo components is worked out, sothat the classification of sub-patterns <1>-<12>is realized.

FIG. 12 shows a case where the gray levels r, g, and b have a magnituderelation of the pattern [1] (r>g>b). Meanwhile, FIG. 13 shows a casewhere ro and yo worked out in the aforesaid pattern [1] correspond toro>yo included in the sub-pattern <1>.

As FIG. 13 illustrates, when ro>yo, it is possible to assume that thegray level yo is a common level between ro and yo. On this account, thegray level of yo would correspond to red-yellow (ry) that is a neutralcolor (orange) between red and yellow. In similar manners, ry, rm, bm,bc, gc, gy are worked out in the color component extraction section 32.

The matrix operation section 33 generates a video signal PS3 made up ofcolor components d1 through d5, in the following manner: an equation (6)is worked out using ro, go, bo, yo, mo, co, wo, ry, rm, bm, bc, gc, andgy figured out in the color component extraction section 32, a matrixoperation corresponding to the number of basic colors of the 5-colordisplay panel 101 is performed, so that the color components of thevideo signal PS2 are reorganized into the color components d1 through d5corresponding to the basic colors of the 5-color display panel 101.$\begin{matrix}\text{[Equation~~6]} & \quad \\{\begin{pmatrix}{d1} \\{d2} \\\vdots \\{d5}\end{pmatrix} = {A_{5 \times 13}\begin{pmatrix}{ro} \\{go} \\{bo} \\{yo} \\{mo} \\{co} \\{wo} \\{ry} \\{rm} \\{bm} \\{bc} \\{gc} \\{gy}\end{pmatrix}}} & (6)\end{matrix}$

In the equation 6, A_(5×13) is a 5×13 matrix, and represented by anequation (7). $\begin{matrix}\text{[Equation~~7]} & \quad \\{A_{5 \times 13}\begin{pmatrix}a_{11} & a_{12} & a_{13} & \ldots & a_{111} & a_{112} & a_{113} \\a_{21} & a_{22} & a_{23} & \ldots & a_{211} & a_{212} & a_{213} \\a_{31} & a_{32} & a_{33} & \ldots & a_{311} & a_{312} & a_{313} \\a_{41} & a_{42} & a_{43} & \ldots & a_{411} & a_{412} & a_{413} \\a_{51} & a_{52} & a_{53} & \ldots & a_{511} & a_{512} & a_{513}\end{pmatrix}} & (7)\end{matrix}$

The elements (matrix coefficients) a_(ij) in the matrix A_(5×13) aredetermined in line with the basic colors of the 5-color display panel101, and are adjusted in line with the adjustment signal. These matrixcoefficients are determined by the matrix generation section 36. Thematrix coefficients can be determined as shown in Table. 5, in a mannersimilar to Embodiment 1. The adjusting parameters (hue, color saturationand brightness) are defined as shown in Table. 6. TABLE 5 ro go bo yo moco wo d1(R) a₁₁ = Vr − Sr a₁₂ = Sg/2 a₁₃ = −Hb a₁₄ = +Hy a₁₅ = Vm − Sm/2− Hm a₁₆ = Sc a₁₇ = 1 d2(G) a₂₁ = 0 a₂₂ = Vg + Sg a₂₃ = −0 a₂₄ = −Hy a₂₅= Sm a₂₆ = +Hc a₂₇ = 1 d3(B) a₃₁ = +Hr a₃₂ = Sg/2 a₃₃ = Vb + Sb a₃₄ = Sya₃₅ = Vm − Sm/2 + Hm a₃₆ = −Hc a₃₇ = 1 d4(Y) a₄₁ = −Hr a₄₂ = +Hg a₄₃ =Sb a₄₄ = Vy − Sy a₄₅ = 0 a₄₆ = 0 a₄₇ = 1 d5(C) a₅₁ = +Sr a₅₂ = −Hg a₅₃ =+Hb a₅₄ = 0 a₅₅ = 0 a₅₆ = Vc − Sc a₅₇ = 1 d1(R) a₁₀ = 0 a₁₉ = 0 a₁₁₀ = 0a₁₁₁ = 0 a₁₁₂ = 0 a₁₁₃ = 0 d2(G) a₂₈ = 0 a₂₀ = 0 a₂₁₀ = 0 a₂₁₁ = 0 a₂₁₂= 0 a₂₁₃ = 0 d3(B) a₃₈ = 0 a₃₉ = 0 a₃₁₀ = 0 a₃₁₁ = 0 a₃₁₂ = 0 a₃₁₃ = 0d4(Y) a₄₈ = 0 a₄₉ = 0 a₄₁₀ = 0 a₄₁₁ = 0 a₄₁₂ = 0 a₄₁₃ = 0 d5(C) a₅₈ = 0a₅₉ = 0 a₅₁₀ = 0 a₅₁₁ = 0 a₅₁₂ = 0 a₅₁₃ = 0 ry rm bm bc gc gy

TABLE 6 COLOR HUE SATULATION BRIGHTNESS RED Hr Sr Vr GREEN Hg Sg Vg BLUEHb Sb Vb YELLOW Hy Sy Vy MAGENTA Hm Sm Vm CYAN Hc Sc Vc

As a matter of course, this set of matrix coefficients is only anexample as described in Embodiment 1. Matrix coefficients for adjustingcolor tones of neutral colors (red-yellow, red-magenta, blue-magenta,blue-cyan, green-cyan, and green-yellow) are also conceivable as anotherexample.

For instance, in a case of a panel in which the brightness of an yellowpixel (D4) is significantly higher than a red pixel (D1), a color amongred-yellow neutral colors, which is closer to red than yellow, looksyellowish as compared to the desired color. To solve this problem, theyellowish tendency in the red-yellow area can be restrained usingadjusting parameters Qry or Qry′, that is, by subtracting Qry×ry from d4or subtracting Qry′×ry. On the other hand, the reddish tendency in thered-yellow can be restrained using an adjusting parameter Pry (bysubtracting Pry×ry from d1).

To realize these adjustments, the matrix coefficients of the matrixA_(5×13) in the equation (6) are set as in Table. 7. The adjustingparameters for adjusting the color tones of neutral colors are definedas in Table. 8. Also, FIG. 14 shows a chromaticity diagram on which thecolors adjusted by these parameters are disposed. TABLE 7 ro go bo yo moco wo d1(R) a₁₁ = Vr − Sr a₁₂ = Sg/2 a₁₃ = −Hb a₁₄ = +Hy a₁₅ = Vm − Sm/2− Hm a₁₆ = Sc a₁₇ = 1 d2(G) a₂₁ = 0 a₂₂ = Vg + Sg a₂₃ = −0 a₂₄ = −Hy a₂₅= Sm a₂₆ = +Hc a₂₇ = 1 d3(B) a₃₁ = +Hr a₃₂ = Sg/2 a₃₃ = Vb + Sb a₃₄ = Sya₃₅ = Vm − Sm/2 + Hm a₃₆ = −Hc a₃₇ = 1 d4(Y) a₄₁ = −Hr a₄₂ = +Hg a₄₃ =Sb a₄₄ = Vy − Sy a₄₅ = 0 a₄₆ = 0 a₄₇ = 1 d5(C) a₅₁ = +Sr a₅₂ = −Hg a₅₃ =+Hb a₅₄ = 0 a₅₅ = 0 a₅₆ = Vc − Sc a₅₇ = 1 d1(R) a₁₈ = −Pry a₁₉ = Prma₁₁₀ = −Qbm a₁₁₁ = 0 a₁₁₂ = 0 a₁₁₃ = −Qgy’ d2(G) a₂₈ = −Qry’ a₂₉ = 0a₂₁₀ = 0 a₂₁₁ = −Qbc’ a₂₁₂ = −Pgc a₂₁₃ = −Pgy d3(B) a₃₈ = 0 a₃₉ = −Qrma₃₁₀ = −Pbm a₃₁₁ = −Pbc a₃₁₂ = −Qgc’ a₃₁₃ = 0 d4(Y) a₄₈ = −Qry a₄₉ = 0a₄₁₀ = 0 a₄₁₁ = 0 a₄₁₂ = 0 a₄₁₃ = −Qgy d5(C) a₅₈ = 0 a₅₉ = 0 a₅₁₀ = 0a₅₁₁ = −Qbc a₅₁₂ = Qgc a₅₁₃ = 0 ry rm bm bc gc gy

TABLE 8 To make red-yellow area reddish Qry, Qry’ To make yellow-greenarea greenish Qgy, Qgy’ To make green-cyan area greenish Qgc, Qgc’ Tomake cyan-blue area bluish Qbc, Qbc’ To make blue-magenta area bluishQbm To make magenta-red area reddish Qrm To make red-yellow areayellowish Pry To make yellow-green area yellowish Pgy To make green-cyanarea incline to cyan Pgc To make cyan-blue area incline to cyan Pbc Tomake blue-magenta area incline to magenta Pbm To make magenta-blue areaincline to magenta Prm

In this manner, also in the color conversion circuit 302, by theadjustment of the matrix coefficients as in the case of Embodiment 1,the adjustment of colors represented by the signal after the conversioncan be performed using intuitively-understandable parameters. In thecolor conversion circuit 302, the color component extraction section 32extracts a greater number of color components as compared to the colorconversion circuit 102 of Embodiment 1 and the color conversion circuit202 of Embodiment 2. On this account, the color conversion circuit 302makes it possible to perform the adjustment in a more detailed manner.

As described above, the color conversion circuit 302 is a color signalconverter that converts a three-primary-color signal to a 5-colorsignal. Since the present embodiment assumes that the multicolor displaypanel 101 has 5-color pixels, the color conversion circuit 102 performsthe conversion to a 5-color signal. In the present invention, however,the multicolor display panel 101 may be a display panel having n-colorpixels corresponding to n colors (n≧4). In such a case, the colorconversion circuit 302 performs the conversion to an n-color signalcorresponding to the number of the colors of the pixels.

The color conversion circuit 302 includes the color component extractionsection 32 serving as a first color signal generation module thatgenerates, by subjecting the three-primary-color signal to isochromaticconversion, an m-color signal made up of m color components (m≧n)including colors equivalent to those of the color components of then-color signal. It is noted that the color components having equivalentcolors are two color components whose positions on a chromaticitydiagram are relatively close to each other and which are sensed assimilar colors, such as R and D1, G and D2, B and D3, Y and D4, and Cand D5 in FIG. 4.

In this manner, in the color conversion circuit 302, the adjustment ofcolors represented by the signal after the conversion can be performedusing intuitively-understandable parameters, as in the case ofEmbodiment 1.

In the color component extraction section 32, m color components aremade up of: primary-color components of the three-primary-color signal;complementary-color components corresponding to the respectiveprimary-color components; neutral color components between theprimary-color components and the complementary color components; and anachromatic color component. With this, as the above-described patterns[1]-[6] and sub-patterns <1>-<12>show, the m-color signal is generatedby performing simple calculations such as subtracting one primary-colorcomponent from another primary-color component.

As in Embodiment 1, the color conversion circuit 302 is further providedwith the matrix generation section 36 serving as a coefficient changemodule that changes matrix coefficients in the matrix operation section33.

The characteristic feature of the color conversion circuit 302 can berephrased as follows: the color conversion circuit 302 is a signalconverter that converts a three-dimensional video signal to ann-dimensional video signal supplied to the multicolor display panel 101including n-color (n≧4) pixels. The color conversion circuit 302 (i)identifies which one of six patterns categorized in accordance with themagnitude relation of gray levels of the three-dimensional video signalis matched with the pattern of the actually-inputted three-dimensionalvideo signal, (ii) extracts a plurality of color components byperforming an operation corresponding to each pattern, and (iii)reorganizes the extracted color components into the input signalsupplied to the multicolor display panel 101. Furthermore, the colorconversion circuit 302 generates a multi-dimensional video signal, using(I) a first module that extracts red (ro), green (go), blue (bo), yellow(yo), cyan (co), magenta (mo), and white (wo) components by identifyingsix patterns from the gray levels of the three-dimensional signal andperforming an operation corresponding to each pattern, and also extractsred-yellow (ry), red-magenta (rm), blue-magenta (bm), blue-cyan (bc),green-cyan (gc), and green-yellow (gy) components by identifying twelvesub-patterns from the aforesaid components, and (II) a second modulethat reorganizes these components, by means of the aforesaid matrixoperation in line with n.

With this color conversion circuit 302, a multi-dimensional video signalcorresponding to a multicolor display apparatus is generated byperforming an operation based on a typically-used three-dimensionalvideo signal.

It is noted that the matrix coefficients in the matrix of the equation(6) may be changed in accordance with the result of the identificationof six patterns and twelve sub-patterns by the color componentextraction section 32.

Also, the components ro, go, bo, yo, mo, co, wo, ry, rm, bm, bc, gc, andgy may be subjected to the matrix operation by the matrix operationsection 33, after being subjected to nonlinear processing.

Now, a variant example of the aforesaid matrix coefficients will bediscussed.

<Auxiliary Illumination by Color Mixing>

When one pixel is divided into parts corresponding to not less than fourcolors, the open area ratio is generally smaller than the open arearatio in a case where one pixel is divided into three colors, so thatthe brightness of each pixel is relatively decreased. As to the partscorresponding to red, green and blue, the decrease of the brightness isusually unavoidable. Meanwhile, as to the parts corresponding to yellow,cyan, and magenta, the decrease of the brightness can be avoided in thefollowing manner.

For instance, when yellow color is displayed, the yellow color isgenerated by performing auxiliary illumination of the R and G pixels, inorder to compensate the brightness of the Y pixel. This is because theyellow color can be generated by additive color mixing of red and green.In similar manners, cyan color can be generated by additive color mixingof green and blue, and magenta can be generated by additive color mixingof red and blue.

To perform this type of adjustment, the matrix coefficients of thematrix A_(5×13) in the equation (6) is set as in Table. 9. The matrixcoefficients of Table. 9 is different from the matrix coefficients inTable. 7 in that Vy is added to a₁₄ and a₂₄, and Vc is added to a₂₆ anda₃₆. The value Vy is an adjusting parameter with which not only the Ypixel but also R and G pixels are used for reproducing yellow color,while the value Vc is an adjusting parameter with which not only the Cpixel but also the G and B pixels are used for reproducing cyan color.It is noted that, since the basic colors of the 5-color display panel101 of the present embodiment do not include magenta, magenta color isalways reproduced by the R and B pixels (see Table. 7). TABLE 9 ro go boyo mo co wo d1(R) a₁₁ = Vr − Sr a₁₂ = Sg/2 a₁₃ = −Hb a₁₄ = Vy + Hy a₁₅ =Vm − Sm/2 − Hm a₁₆ = Sc a₁₇ = 1 d2(G) a₂₁ = 0 a₂₂ = Vg + Sg a₂₃ = −0 a₂₄= Vy − Hy a₂₅ = Sm a₂₆ = Vc + Hc a₂₇ = 1 d3(B) a₃₁ = +Hr a₃₂ = Sg/2 a₃₃= Vb + Sb a₃₄ = Sy a₃₅ = Vm − Sm/2 + Hm a₃₆ = Vc − Hc a₃₇ = 1 d4(Y) a₄₁= −Hr a₄₂ = +Hg a₄₃ = Sb a₄₄ = Vy − Sy a₄₅ = 0 a₄₆ = 0 a₄₇ = 1 d5(C) a₅₁= +Sr a₅₂ = −Hg a₅₃ = +Hb a₅₄ = 0 a₅₅ = 0 a₅₆ = Vc − Sc a₅₇ = 1 d1(R)a₁₈ = −Pry a₁₉ = Prm a₁₁₀ = −Qbm a₁₁₁ = 0 a₁₁₂ = 0 a₁₁₃ = −Qgy’ d2(G)a₂₈ = −Qry’ a₂₉ = 0 a₂₁₀ = 0 a₂₁₁ = −Qbc’ a₂₁₂ = −Pgc a₂₁₃ = −Pgy d3(B)a₃₈ = 0 a₃₉ = −Qrm a₃₁₀ = −Pbm a₃₁₁ = −Pbc a₃₁₂ = −Qgc’ a₃₁₃ = 0 d4(Y)a₄₈ = −Qry a₄₉ = 0 a₄₁₀ = 0 a₄₁₁ = 0 a₄₁₂ = 0 a₄₁₃ = −Qgy d5(C) a₅₈ = 0a₅₉ = 0 a₅₁₀ = 0 a₅₁₁ = −Qbc a₅₁₂ = −Qgc a₅₁₃ = 0 ry rm bm bc gc gy

Note that, this auxiliary illumination by the additive color mixing isparticularly effective in the case of reproducing yellow color. This isbecause, in a typical image, the yellow color must particularly be thickand have a high brightness. Pointer clarifies this in his article (M. R.Pointer, The Gamut of Real Surface Colors, COLOR research andapplication Vol.5 Number 3, Fall (1980) p.145). In this article, alltypes of colors and brightness in existence are represented as points ona color space. According to the essay, while cyan and magenta do notrequire a high brightness, yellow requires a high brightness.

In the case where the brightness of yellow color is reproduced not onlyby the Y pixel but also by the R and G pixels, the yellowish tendency inthe red-yellow area can be reduced preferably by increasing the ratio ofthe subtraction of Qry′×ry from d2 as compared to the subtraction ofQry×ry from d4. In short, it is preferable that Qry<Qry′. With this, thedecrease of the color reproduction range of highly-bright yellow colorcan be restrained.

<Making Matrix Coefficient into Function>

In the adjustments above, the matrix coefficients of the matrix A_(5×13)in the equation (6) are constants that can be changed by mean of theadjustment signal. Alternatively, these matrix coefficients may be madeinto functions. The following will describe a case where the matrixcoefficients are made into functions (i.e. functionalization).

First, the functionalization of the matrix coefficients performed inorder to keep a gray level to be less than the upper allowable limit (1)of the gray levels as much as possible will be discussed.

For instance, provided that the matrix coefficients in Table. 7 areused, if the adjusting parameter Vr is not less than 1 in the term Vr×roin the calculation for figuring out d1, the result of the term Vr×roexceeds the upper allowable limit (1) of d1, as shown in FIG. 15. Sinced1 exceeding the maximum value (1) is set at 1 by the clipping, the graylevels in this range cannot be reproduced.

To solve this problem, in stead of the adjusting parameter Vr, anadjusting function Fr(ro) (Fr(ro) monotonously increases with respect toro, and Fr(1)=1; see FIG. 15). With this, it is possible to keep d1 tobe not more than the maximum value (1) as much as possible.

To perform this adjustment, the matrix coefficients of the matrixA_(5×13) in the equation (6) is set as in Table. 10. The matrixcoefficients in Table. 10 is different from the matrix coefficients inTable. 7 in that, instead of the adjusting parameters Vr, Vg, Vb, Vy,Vm, and Vc, adjusting functions Fr(ro), Fg(go), Fb(bo), Fy(yo), Fm(mo),and FC(co) are used in the matrix coefficients in Table. 10. Theseadjusting functions Fr(ro), Fg(go), Fb(bo), Fy(yo), Fm(mo), and FC(co)monotonously increase with respect to ro, go, bo, yo, mo, and co,respectively, and, Fr(1)=1, Fg(1)=1, Fb(1)=1, Fy(1)=1, Fm(1)=1, Fc(1)=1.

These adjusting functions Fr(ro), Fg(go), Fb(bo), Fy(yo), Fm(mo), andFC(co) may be predetermined functions, or may be functions adjusted bythe adjustment signal. TABLE 10 ro go bo yo mo co wo d1(R) a₁₁ = Fr − Sra₁₂ = Sg/2 a₁₃ = −Hb a₁₄ = +Hy a₁₅ = Fm − Sm/2 − Hm a₁₆ = Sc a₁₇ = 1d2(G) a₂₁ = 0 a₂₂ = Fg + Sg a₂₃ = −0 a₂₄ = −Hy a₂₅ = Sm a₂₆ = +Hc a₂₇ =1 d3(B) a₃₁ = +Hr a₃₂ = Sg/2 a₃₃ = Fb + Sb a₃₄ = Sy a₃₅ = Fm − Sm/2 + Hma₃₆ = −Hc a₃₇ = 1 d4(Y) a₄₁ = −Hr a₄₂ = +Hg a₄₃ = Sb a₄₄ = Fy − Sy a₄₅ =0 a₄₆ = 0 a₄₇ = 1 d5(C) a₅₁ = +Sr a₅₂ = −Hg a₅₃ = +Hb a₅₄ = 0 a₅₅ = 0a₅₆ = Fc − Sc a₅₇ = 1 d1(R) a₁₈ = −Pry a₁₉ = Prm a₁₁₀ = −Qbm a₁₁₁ = 0a₁₁₂ = 0 a₁₁₃ = −Qgy’ d2(G) a₂₈ = −Qry’ a₂₉ = 0 a₂₁₀ = 0 a₂₁₁ = −Qbc’a₂₁₂ = −Pgc a₂₁₃ = −Pgy d3(B) a₃₈ = 0 a₃₉ = −Qrm a₃₁₀ = −Pbm a₃₁₁ = −Pbca₃₁₂ = −Qgc’ a₃₁₃ = 0 d4(Y) a₄₈ = −Qry a₄₉ = 0 a₄₁₀ = 0 a₄₁₁ = 0 a₄₁₂ =0 a₄₁₃ = −Qgy d5(C) a₅₈ = 0 a₅₉ = 0 a₅₁₀ = 0 a₅₁₁ = −Qbc a₅₁₂ = −Qgca₅₁₃ = 0 ry rm bm bc gc gy

Now, a variant example of the aforesaid auxiliary illumination by colormixing (see Table. 10) is discussed.

For instance, a chromaticity point of a color reproduced by additivecolor mixing of R and G is on the lower color saturation side ascompared to a chromaticity point of a color reproduced sorely by a Ypixel. For this reason, when the adjustment of the brightness by colormixing is performed, an actual color reproduction range is at timesnarrower than a color reproduction range that is originally realized bythe chromaticity points of pixels. This is because, as shown in FIG. 16,the chromaticity of the yellow color generated by the additive colormixing of R and G is on the white side as compared to the chromaticityof the Y pixel.

This decrease of the color reproduction range can be restrained bysetting the matrix coefficients of the matrix A_(5×13) in the equation(6), in the following manner.

For instance, an yellow color that has low brightness and can bereproduced sorely by the Y pixel is reproduced sorely by the Y pixel,while an yellow color having a higher brightness is reproduced byenhancing the yellow color by performing the additive color mixing of Rand G.

With this, while an yellow color with a low brightness is reproduced inline with the original color reproduction range, an yellow color with ahigh brightness is also reproduced even if the color reproduction rangeis narrowed to some extent. This arrangement can be applicable forreproducing cyan and magenta colors as well.

To perform this type of adjustment, the matrix coefficients of thematrix A_(5×13) in the equation (6) is set as in Table. 11. The matrixcoefficients in Table 11. is different from the matrix coefficients inTable 10. in that, in the matrix coefficients in Table 11, an adjustingfunction Fy′(yo) is added to a₁₄ and a₂₄, while an adjusting functionFc′(co) is added to a₂₆ and a₃₆. TABLE 11 ro go bo yo mo co wo d1(R) a₁₁= Fr − Sr a₁₂ = Sg/2 a₁₃ = −Hb a₁₄ = Fy’ + Hy a₁₅ = Fm − Sm/2 − Hm a₁₆ =Sc a₁₇ = 1 d2(G) a₂₁ = 0 a₂₂ = Fg + Sg a₂₃ = −0 a₂₄ = Fy’ − Hy a₂₅ = Sma₂₆ = Fc’ + Hc a₂₇ = 1 d3(B) a₃₁ = +Hr a₃₂ = Sg/2 a₃₃ = Fb + Sb a₃₄ = Sya₃₅ = Fm − Sm/2 + Hm a₃₆ = Fc’ − Hc a₃₇ = 1 d4(Y) a₄₁ = −Hr a₄₂ = +Hga₄₃ = Sb a₄₄ = Fy − Sy a₄₅ = 0 a₄₆ = 0 a₄₇ = 1 d5(C) a₅₁ = +Sr a₅₂ = −Hga₅₃ = +Hb a₅₄ = 0 a₅₅ = 0 a₅₆ = Fc − Sc a₅₇ = 1 d1(R) a₁₈ = −Pry a₁₉ =Prm a₁₁₀ = −Qbm a₁₁₁ = 0 a₁₁₂ = 0 a₁₁₃ = −Qgy’ d2(G) a₂₈ = −Qry’ a₂₉ = 0a₂₁₀ = 0 a₂₁₁ = −Qbc’ a₂₁₂ = −Pgc a₂₁₃ = −Pgy d3(B) a₃₈ = 0 a₃₉ = −Qrma₃₁₀ = −Pbm a₃₁₁ = −Pbc a₃₁₂ = −Qgc’ a₃₁₃ = 0 d4(Y) a₄₈ = −Qry a₄₉ = 0a₄₁₀ = 0 a₄₁₁ = 0 a₄₁₂ = 0 a₄₁₃ = −Qgy d5(C) a₅₈ = 0 a₅₉ = 0 a₅₁₀ = 0a₅₁₁ = −Qbc a₅₁₂ = −Qgc a₅₁₃ = 0 ry rm bm bc gc gy

In this table, the adjusting functions Fy(yo) and Fy′(yo) are, forexample, set as shown in FIGS. 17 and 18. That is, in a case where anyellow color is reproduced, the yellow color is reproduced sorely by theY pixel if the value of yo is less than a threshold Ysh, while theyellow color is enhanced by the color mixing of R and G if the value ofyo is not less than the threshold Ysh. This threshold Ysh is a graylevel of yo when the brightness of the Y pixel is at the maximum. Theadjusting functions Fc(co) and Fc′(co) are set in a similar manner.

VARIANT EXAMPLE

(Subtractive Color Mixing)

The embodiments above presuppose that an additive color mixing signal isused, primary-color components of the three-primary-color signal arered, green and blue, complementary color components are yellow, magenta,and cyan, and an achromatic color component is white.

The present invention is applicable not only when the additive colormixing signal is used but also when a subtractive color mixing signal isused. In the latter case, primary-color components of thethree-primary-color signal are yellow, magenta, and cyan, complementarycolor components are red green, and blue, and an achromatic colorcomponent is white.

When the subtractive color mixing signal is adopted, the color componentextraction section 12 of Embodiment 1 or 2 performs the followingoperation: provided that a video signal PS1 is a YMC signal andrepresents gray levels y, m, and c (0≦y, m, c≦1), the color componentextraction section 12 works out gray levels ro, go, bo, yo, mo, co, andwo of red, green, blue, yellow, magenta, cyan, and white colorcomponents, in the following manner:

[1] In a case where y≧m≧c,ro=(m−c)yo=(y−m)go=bo=mo=co=0wo=1−y

[2] In a case where y≧c>m,go=(c−m)yo=(y−c)ro=bo=mo=co=0wo=1−y

[3] In a case where c>y≧m,go=(y−m)co=(c−y)ro=bo=yo=mo=0wo=1−c

[4] In a case where c>m>y,bo=(m−y)co=(c−m)ro=go=yo=mo=0wo=1−c

[5] In a case where m≧c>y,bo=(c−y)mo=(m−c)ro=go=yo=co=0wo=1−m

[6] In a case where m>y≧c,ro=(y−c)mo=(m−y)go=bo=yo=mo=0wo=1−m

The matrix operation section 13 or 23 in Embodiment 1 or 2 generates avideo signal PS3 made up of d1 through d5 or d1 through d4, by workingout the equation (1) as in Embodiment 1 or 2, using ro, go, bo, yo, mo,co, and wo figured out by the color component extraction section 12. Thematrix coefficients in the equation (1) are set in a manner similar tothose in Embodiment 1 or 2.

When the subtractive color mixing signal is adopted, the color componentextraction section 32 of Embodiment 3 performs the following operation:provided that a video signal PS1 is a YMC signal and represents graylevels y, m, and c (0≦y, m, c≦1), the color component extraction section32 works out gray levels ro, go, bo, yo, mo, co, wo, ry, rm, bm, bc, gc,and gy of red, green, blue, yellow, magenta, cyan, white, red-yellow,red-magenta, blue-magenta, blue-cyan, green-cyan, and green-yellow colorcomponents, in the following manner:

[1] In a case where y≧m≧c,ro=(m−c)yo=(y−m)go=bo=mo=co=0wo=1−y

-   -   <1> if ro≧yo, ry=yo    -   <2> if ro<yo, ry=ro        gy=gc=bc=bm=rm=0

[2] In a case where y≧c>m,go=(c−m)yo=(y−c)ro=bo=mo=co=0wo=1−y

-   -   <3> if go≧yo, gy=yo    -   <4> if go<yo, gy=go        ry=gc=bc=bm=rm=0

[3] In a case where c>y≧m,go=(y−m)co=(c−y)ro=bo=yo=mo=0wo=1−c

-   -   <5> if go≧co, gc=co    -   <6> if go<co, gc=co        ry=gy=bc=bm=rm=0

[4] In a case where c>m>y,bo=(m−y)co=(c−m)ro=go=yo=mo=0wo=1−c

-   -   <7> if bo≧co, bc=co    -   <8> if bo<co, bc=bo        ry=gy=gc=bm=rm=0

[5] In a case where m≧c>y,bo=(c−y)mo=(m−c)ro=go=yo=co=0wo=1−m

-   -   <9> if bo≧mo, bm=mo    -   <10> if bo<mo, bm=bo        ry=gy=gc=bc=rm=0

[6] In a case where m>y≧c,ro=(y−c)mo=(m−y)go=bo=yo=mo=0wo=1−m

-   -   <11> if ro≧mo, rm=mo    -   <12> if ro<yo, rm=ro        ry=gy=gc=bc=bm=0

The matrix operation section 33 of Embodiment 3 generates a video signalPS3 made up of d1 through d5, by, as in Embodiment 3, working out theequation (6) using ro, go, bo, mo, co, wo, ry, rm, bm, bc, gc, and gyfigured out by the color component extraction section 32. The matrixcoefficients in the equation (6) are set in a manner similar toEmbodiment 1.

(Calculation in Color Component Extraction Section)

Each of the color component extraction sections 12 and 32 adopted in theaforesaid embodiments extracts color components by identifying 6patterns with reference to the magnitude relation of r, g, b or y, m, c,and calculating a difference corresponding to each pattern. However, thecolor extraction is not necessarily performed in this way. The followingis an example of another color component extraction method.

For instance, the color component extraction can be performed by thecalculation below. Color components ro, go, bo, yo, mo, co, and wo areworked out from inputted r, g, and b, in the following manner.rg=r−grb=r−bgr=g−r

-   -   gb=g−b        br=b−r        bg=b−g

Each of rg, rb, gr, gb, br, and bg is set at 0 if the value is negative.ro=min(rg, rb)go=min(gr, gb)bo=min(br, bg)yo=min(rb, gb)mo=min(rg, bg)co=min(gr, br)wo=min(r, g, b)

(In these equations, the function min( ) returns the smallest value inthe bracket.)

These components worked out above can be used as the values used in theabove-described embodiments.

For instance, in a case where r>g>b, rg, rb, and gb are positive whilegr, br, and bg are negative. Since a negative value is set at 0, gr, br,and bg are 0. Then, as the component ro, the smaller one of rg and rb ischosen. Since r>g>b, rg is chosen in this case. As a result,ro=rg=(r−g). In a similar manner, yo=(g−b) and wo−b, while the remainingcomponents are 0 because one of the values in each function min( ) is 0.

In this manner, the color component extraction can be realized withoutidentifying 6 patterns from the magnitude relation of r, g, and b.

As a matter of course, it is possible to generate neutral colors betweenthe color components by further identifying sub-patterns as in the caseof Embodiment 3.

The color component extraction can be realized also in the case of thesubtractive color mixing, using the following calculation.ym=y−myc=y−cmy=m−ymc=m−ccy=c−ycm=c−m

Each of ym, yc, my, mc, cy, and cm is set at 0 if the value is negative.ro=min(yc, mc)go=min(ym, cm)bo=min(my, cy)yo=min(ym, yc)mo=min(my, mc)co=min(cy, cm)wo=min(1−y, 1−m, 1−c)

(In these equations, the function min( ) returns the smallest value inthe bracket.)

The color components can be extracted as above.

(Application to Apparatuses Other Than Display Apparatus)

In Embodiments 1-3, the color conversion circuit 102, 202, or 302 as thecolor signal converter of the present invention is used for a colordisplay apparatus. In addition to this, the present invention can beadopted to various types of apparatuses that require the conversion of athree-primary-color signal to a n-color signal (n≧4). For instance, thecolor signal converter of the present invention can be used for imageforming apparatuses such as printers and photocopiers.

(Color Signal Conversion Program)

The functional blocks of the color conversion circuit 102, 202, and 302of Embodiments 1-3, i.e. the inverse gamma correction section 11, thematrix operation sections 13 and 23, the clipping section 14, the gammacorrection section 15, and the matrix generation sections 16 and 26 canbe realized not only by hardware but also partially or entirely bysoftware.

In a case where the aforesaid functional blocks are realized bysoftware, an arrangement equivalent to the color conversion circuit 102,202, or 302 is realized using a computer. This computer includes a CPU(Central Processing Unit) for executing various types of programs and aRAM (Random Access Memory) serving as a work area for executing aprogram. On this computer, a color signal conversion program forrealizing the aforesaid functional blocks is run, so that the computeroperates as the functional blocks.

The color signal conversion program may be supplied from a storagemedium to the computer, or may be supplied to the computer via acommunications network.

The storage medium storing the color signal conversion program may bedetachable from the computer or may be incorporated into the computer.The storage medium may be attached to the computer in such a manner asto allow the computer to directly read out program code, or may beprovided as an external storage device that allows the computer to readout program code via a program reading device.

Examples of the storage medium are: tapes such as a magnetic tape and acassette tape; magnetic disks such as a flexible disk and a hard disk;disks such as a CD-ROM, MO, MD, DVD, and CD-R; cards such as an IC card(including a memory card) and an optical card; or a semiconductor memorysuch as a mask ROM, an EPROM (electrically programmable read onlymemory), EEPROM (electrically erasable programmable read only memory),and a flash ROM.

The color signal conversion program is transmitted via a communicationsnetwork, in the form of carrier wave or a data signal row in which theprogram code is embodied through electronic transmission.

The invention being thus described, it will be obvious that the same waymay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

As described above, a color signal conversion apparatus of the presentinvention, which converts a three-primary-color signal to an n-colorsignal (n≧4), comprises: a first color signal generation module forgenerating, by subjecting the three-primary-color signal to isochromaticconversion, an m-color signal made up of m color components (m≧n)including respective color components that are equivalent in terms ofcolor to color components of the n-color signal; and a second colorsignal generation module for generating the color components of then-color signal, by performing linear combination of the color componentsof the m-color signal.

A color signal conversion method of the present invention, forconverting a three-primary-color signal to an n-color signal (n≧4),comprises the steps of: generating, by subjecting thethree-primary-color signal to isochromatic conversion, an m-color signalmade up of m color components (m≧n) including respective colorcomponents that are equivalent in terms of color to color components ofthe n-color signal; and generating the color components of the n-colorsignal, by performing linear combination of the color components of them-color signal.

According to the above-described arrangement and method, athree-primary-color signal that is an original signal is subjected toisochromatic conversion, generating an m-color signal made up of m colorcomponents (m≧n) which are equivalent in terms of color with colorcomponents of a targeted n-color signal. The isochromatic conversion isperformed in such a manner that a combination of color componentsrepresenting a particular color is converted to a combination of othercolor components, without changing the represented color. The colorcomponents having equivalent colors are two color components whosepositions on a chromaticity diagram are relatively close to each otherand which are sensed as similar colors. The color components havingequivalent colors include two identical color components whose positionson the chromaticity diagram are identical with each other.

According to the above-described arrangement and method, furthermore,the color components of the n-color signal generated as a result of theconversion are generated by the linear combination of the colorcomponents of the m-color signal generated as above. The linearcombination of the color components is performed in such a manner thatmultiplication of coefficients and addition are performed with respectto each color component.

When the color components of the n-color signal are generated by thelinear combination of the color components of the m-color signal,intuitively-understandable parameters are used for adjusting the colorsrepresented by the n-color signal, and the coefficients of the linearcombination are determined by simple calculations of these parameters(see Tables. 1-8). As the parameters, it is possible to adopt, forinstance, values (cf. Tables 2, 4, and 6) indicating hue, colorsaturation, and brightness of each color component of the m-color signalor n-color signal and the values (cf. Table. 8) that indicate, in aneutral color between the color components, which one of the colorcomponents is enhanced.

In this manner, the above-described arrangement and method makes itpossible to perform the adjustment of colors represented by the n-colorsignal after the conversion, by means of intuitively-understandableparameters.

The aforesaid color signal conversion apparatus of the present inventionpreferably includes a coefficient change module for changingcoefficients of the linear combination performed by the second colorsignal generation module.

According to this arrangement, the coefficients for the linearcombination by which the color components of the n-color signal aregenerated can be changed by the coefficient change module. Thisadjustment may be performed at the time of manufacture by an adjustingdevice incorporated into the color signal conversion apparatus. However,if the coefficient change module is incorporated into the color signalconversion apparatus as above, the adjustment can be performed at anytime. In this manner, the foregoing arrangement allows the user toperform the adjustment at any time.

The aforesaid color signal conversion apparatus of the present inventionis preferably arranged in such a manner that, in the first color signalgeneration module, said m color components are made up of: primary colorcomponents of the three-primary-color signal; complementary colorcomponents corresponding to the primary color components, respectively;and an achromatic color component.

According to this arrangement, the m-color signal can be generated byperforming simple calculations such as subtracting one primary-colorcomponent from another primary-color component.

The aforesaid color signal conversion apparatus of the present inventionmay be arranged in such a manner that, in the first color signalgeneration module, said m color components are made up of: primary colorcomponents of the three-primary-color signal; complementary colorcomponents corresponding to the primary color components, respectively;neutral color components between the primary color components and thecomplementary color components; and an achromatic color component.

This arrangement makes it possible to perform the adjustment in a moresubtle manner, because the adjustment is performed additionally usingthe neutral components.

If the three-primary-color signal is an additive color mixing signal,the following may hold true: the primary color components are red,green, and blue components, the complementary color components areyellow, magenta, and cyan components, and the achromatic color componentis a white component.

If the three-primary-color signal is a subtractive color mixing signal,the following may hold true: the primary color components are yellow,magenta, and cyan components, the complementary color components arered, green, and blue components, and the achromatic color component is awhite component.

The aforesaid color signal conversion apparatus of the present inventionmay further comprise an inverse gamma correction module for performinginverse gamma correction on the three-primary-color signal having beensubjected to gamma correction, and then supplying thethree-primary-color signal to the first color signal generation module.

In this arrangement, the three-primary-color signal having beensubjected to the gamma correction can be subjected to the inverse gammacorrection, before performing the above-described process. In thethree-primary-color signal having been subjected to the gammacorrection, the relationship between the gray level and brightness isnonlinear. Performing, as described above, the inverse gamma correctionbeforehand, the relationship between the gray level and brightness iscaused to be linear. On this account, the signal conversion is performedin a more suitable manner.

The aforesaid color signal conversion apparatus of the present inventionmay further comprise a gamma correction module for subjecting then-color signal to the gamma correction.

In the arrangement above, the n-color signal generated as a result ofthe conversion is subjected to the gamma correction, in line with thegamma characteristics of a display panel on a stage subsequent to thecolor signal conversion apparatus.

A display unit of the present invention includes: one of theabove-described color signal converters; and a display panel havingn-color pixels corresponding to the color components of the n-colorsignal.

According to this arrangement, a display unit in which the adjustment ofdisplay colors can be performed using intuitively-understandableparameters is realized thanks to the above-described color signalconversion apparatus.

The aforesaid display unit of the present invention may be arranged insuch a manner that, color components of the n-color signal include afirst color component, a second color component, and a third colorcomponent obtained by performing color mixing of the first and secondcolor components, color components of the m-color signal includes athird equivalent color component that is equivalent in terms of color tothe third color component, and in a case where the third equivalentcolor component of the m-color signal is reproduced by the displaypanel, auxiliary illumination by means of pixels corresponding to thefirst and second color components is performed in order to enhanceillumination by a pixel corresponding to the third color component.

According to this arrangement, the pixels corresponding to the first andsecond color components perform the auxiliary illumination, so that thethird component is obtained as a result of the color mixing, and theillumination of the pixel corresponding to the third color component isenhanced. With this, even when the brightness of the pixel correspondingto the third color component is insufficient, the third color componentis reproduced with a sufficient brightness.

The aforesaid display unit of the present invention may be arranged insuch a manner that, the auxiliary illumination is not performed in acase where a gray level of the third equivalent color component of them-color signal is low, while the auxiliary illumination is performed ina case where the gray level of the third equivalent color component ishigh.

In general, the third color component obtained as a result of theauxiliary illumination performed by the pixels corresponding to thefirst and second color components has a color saturation lower than thatof the third color component obtained by the illumination of the pixelcorresponding to the third color component. On this account, theauxiliary illumination is not performed when the pixel corresponding tothe third color component is sufficiently bright, i.e. when the graylevel of the third color component is low. With this, the decrease ofthe color saturation can be avoided.

It is particularly preferable that the first and second color componentsbe red and green while the third color component be yellow. This isbecause, in a typical image, the yellow color must particularly be thickand have a high brightness.

A color signal conversion program of the present invention realizes, bya computer, one of the foregoing color signal conversion apparatuses.This color signal conversion program can be implemented as a program forcausing a computer to operate as the aforesaid module. Acomputer-readable storage medium of the present invention can store theaforesaid color signal conversion program.

A color display apparatus of the present invention, for displaying acolor image, comprises: n-color pixels corresponding to n colorcomponents (n≧4) of which the color image is made up, wherein, said ncolor components include a first color component, a second colorcomponent, and a third color component obtained by performing colormixing of the first and second color components, and in a case where thethird equivalent color component of the m-color signal is reproduced bythe display panel, auxiliary illumination by means of pixelscorresponding to the first and second color components is performed inorder to enhance illumination by a pixel corresponding to the thirdcolor component.

A color display method for displaying a color image is arranged in sucha manner that n-color pixels corresponding to n color components (n≧4)of which the color image is made up is used, said n color componentsinclude a first color component, a second color component, and a thirdcolor component obtained by performing color mixing of the first andsecond color components, and in a case where the third equivalent colorcomponent of the m-color signal is reproduced, auxiliary illumination bymeans of pixels corresponding to the first and second color componentsis performed in order to enhance illumination by a pixel correspondingto the third color component.

According to the above-described arrangement and method, the pixelscorresponding to the first and second color components perform theauxiliary illumination, so that the third component is obtained as aresult of the color mixing, and the illumination of the pixelcorresponding to the third color component is enhanced. With this, evenwhen the brightness of the pixel corresponding to the third colorcomponent is insufficient, the third color component is reproduced witha sufficient brightness.

The aforesaid color display apparatus of the present invention may bearranged in such a manner that, the auxiliary illumination is notperformed in a case where a gray level of the third equivalent colorcomponent of the m-color signal is low, while the auxiliary illuminationis performed in a case where the gray level of the third equivalentcolor component is high.

In general, the third color component obtained as a result of theauxiliary illumination performed by the pixels corresponding to thefirst and second color components has a color saturation lower than thatof the third color component obtained by the illumination of the pixelcorresponding to the third color component. On this account, theauxiliary illumination is not performed when the pixel corresponding tothe third color component is sufficiently bright, i.e. when the graylevel of the third color component is low. With this, the decrease ofthe color saturation can be avoided.

It is particularly preferable that the first and second color componentsbe red and green while the third color component be yellow. This isbecause, in a typical image, the yellow color must particularly be thickand have a high brightness.

According to the present invention, an RGB or YMC input color signal canbe converted to a video signal for a multi-color display apparatus.Furthermore, on the occasion of the conversion, the adjustment of hue,color saturation, and brightness of the colors can be performed, so thatthe resultant video signal is suitable for the multi-color displayapparatus. The present invention is, therefore, suitably adopted to amulti-color display apparatus having pixels corresponding to not lessthan four colors, such as a monitor for PC, a liquid crystal TV set, aliquid crystal projector, and a display panel of a mobile phone.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe included within the scope of the following claims.

1. A color signal converter that converts a three-primary-color signalto an n-color signal (n≧4), the color signal converter comprising: afirst color signal generation module for generating, by subjecting thethree-primary-color signal to isochromatic conversion, an m-color signalmade up of m color components (m≧n) including respective colorcomponents that are equivalent in terms of color to color components ofthe n-color signal; and a second color signal generation module forgenerating the color components of the n-color signal, by performinglinear combination of the color components of the m-color signal.
 2. Thecolor signal converter as defined in claim 1, further comprising acoefficient change module for changing coefficients of the linearcombination performed by the second color signal generation module. 3.The color signal converter as defined claim 1, wherein, in the firstcolor signal generation module, said m color components are made up of:primary color components of the three-primary-color signal;complementary color components corresponding to the primary colorcomponents, respectively; and an achromatic color component.
 4. Thecolor signal converter as defined in claim 1, wherein, in the firstcolor signal generation module, said m color components are made up of:primary color components of the three-primary-color signal;complementary color components corresponding to the primary colorcomponents, respectively; neutral color components between the primarycolor components and the complementary color components; and anachromatic color component.
 5. The color signal converter as defined inclaim 3, wherein, the primary color components are red, green, and bluecomponents, the complementary color components are yellow, magenta, andcyan components, and the achromatic color component is a whitecomponent.
 6. The color signal converter as defined in claim 3, wherein,the primary color components are yellow, magenta, and cyan components,the complementary color components are red, green, and blue components,and the achromatic color component is a white component.
 7. The colorsignal converter as defined in claim 1, further comprising an inversegamma correction module for performing inverse gamma correction on thethree-primary-color signal having been subjected to gamma correction,and then supplying the three-primary-color signal to the first colorsignal generation module.
 8. The color signal converter as defined inclaim 1, further comprising a gamma correction module for subjecting then-color signal to the gamma correction.
 9. A display unit, comprising:the color signal converter defined in claim 1; and a display panelhaving n-color pixels corresponding to the color components of then-color signal.
 10. The display unit as defined in claim 9, wherein,color components of the n-color signal include a first color component,a second color component, and a third color component obtained byperforming color mixing of the first and second color components, colorcomponents of the m-color signal includes a third equivalent colorcomponent that is equivalent in terms of color to the third colorcomponent, and in a case where the third equivalent color component ofthe m-color signal is reproduced by the display panel, auxiliaryillumination by means of pixels corresponding to the first and secondcolor components is performed in order to enhance illumination by apixel corresponding to the third color component.
 11. The display unitas defined in claim 10, wherein, the auxiliary illumination is notperformed in a case where a gray level of the third equivalent colorcomponent of the m-color signal is low, while the auxiliary illuminationis performed in a case where the gray level of the third equivalentcolor component is high.
 12. The display unit as defined in claim 10,wherein, the first color component is red, the second color component isgreen, and the third color component is yellow.
 13. A color signalconversion program for realizing the color signal converter defined inclaim 1 by a computer, the color signal conversion program causing thecomputer to function as the first color signal generation module and thesecond color signal generation module.
 14. A computer-readable storagemedium, storing the color signal conversion program defined in claim 13.15. A color signal conversion method for converting athree-primary-color signal to an n-color signal (n≧4), the methodcomprising the steps of: generating, by subjecting thethree-primary-color signal to isochromatic conversion, an m-color signalmade up of m color components (m≧n) including respective colorcomponents that are equivalent in terms of color to color components ofthe n-color signal; and generating the color components of the n-colorsignal, by performing linear combination of the color components of them-color signal.
 16. A color display apparatus for displaying a colorimage, comprising: n-color pixels corresponding to n color components(n≧4) of which the color image is made up, wherein, said n colorcomponents include a first color component, a second color component,and a third color component obtained by performing color mixing of thefirst and second color components, and in a case where the thirdequivalent color component of the m-color signal is reproduced by thedisplay panel, auxiliary illumination by means of pixels correspondingto the first and second color components is performed in order toenhance illumination by a pixel corresponding to the third colorcomponent.
 17. The color display apparatus as defined in claim 16,wherein, the auxiliary illumination is not performed in a case where agray level of the third equivalent color component of the m-color signalis low, while the auxiliary illumination is performed in a case wherethe gray level of the third equivalent color component is high.
 18. Thecolor display apparatus as defined in claim 16, wherein, the first colorcomponent is red, the second color component is green, and the thirdcolor component is yellow.
 19. A color display method for displaying acolor image, wherein, n-color pixels corresponding to n color components(n≧4) of which the color image is made up is used, said n colorcomponents include a first color component, a second color component,and a third color component obtained by performing color mixing of thefirst and second color components, and in a case where the thirdequivalent color component of the m-color signal is reproduced,auxiliary illumination by means of pixels corresponding to the first andsecond color components is performed in order to enhance illumination bya pixel corresponding to the third color component.